JP2005151661A - Thermoelectric generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric generator wherein optimum output power is obtained almost all the time through appropriate setting of initial values and the like. <P>SOLUTION: The thermoelectric generator is so designed that high-temperature fluid discharged from a high-temperature fluid source is utilized to generate power. The thermoelectric generator comprises: a thermoelectric element that converts the thermal energy of the high-temperature fluid into electrical energy; and a controlling means that controls the output of the thermoelectric element with an initial current value determined according to the state of the operation of the high-temperature fluid source. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention belongs to the technical field of thermoelectric generators.

  Conventionally, by using high-temperature exhaust gas discharged from automobile engines, factory waste heat, incinerator waste heat, etc., thermoelectric power that can be used by converting a part of the heat energy into electrical energy. A power generation device is known. This thermoelectric generator has a structure in which elements made of two different materials, such as a P-type semiconductor element and an N-type semiconductor element, are joined, and one side surface thereof is exposed to a high temperature and the other side surface is exposed to a low temperature. As a result, a thermoelectromotive force due to the temperature difference is generated.

  Such a thermoelectric generator has a large temperature dependency. In other words, the output power that can be extracted from the thermoelectric generator varies greatly depending on the temperature on the high temperature side and the temperature on the low temperature side. Along with this, it is known that the maximum output point of the thermoelectric generator is also greatly affected by temperature. However, when the thermoelectric generator is mounted on an automobile or the like, generally, the automobile is traveling on a highway or traveling on an urban area. Since the temperature of the high-temperature fluid (exhaust gas in the case of an engine) discharged from the fluid source changes every moment, it has been difficult to maintain the output power of the thermoelectric generator optimally.

  Therefore, conventionally, in order to deal with such problems, for example, a thermoelectric power generation charging device as disclosed in Patent Document 1 has been proposed. In Patent Document 1, the maximum output characteristic is obtained by measuring the temperature on the high temperature side and the low temperature side of the thermoelectric element and determining the optimum current value from the output characteristic of the thermoelectric element at the measured temperature. Technology is disclosed. Also, although it is related to solar cells instead of thermoelectric generators, it is known that the output characteristics change under the influence of solar radiation and element temperature in solar cells, so a technology based on the same idea, For example, it is disclosed in Patent Documents 2 and 3.

JP-A-6-22572 JP-A-6-110571 JP-A-8-227324

  However, the conventional thermoelectric generator has the following problems. That is, according to Patent Document 1, it seems that the maximum output point that can be achieved in the thermoelectric element can always be suitably maintained while corresponding to the temperature changing every moment. However, a certain amount of control is required between the time when the thermoelectric generator is actually operated and the time when it can realize an appropriate output power corresponding to that temperature. In general, it takes a considerable amount of time. Therefore, depending on the contents of the control, the output power of the thermoelectric element may not be optimized. This is because the high temperature side temperature and the low temperature side temperature may have changed to different values during the lapse of the time. In this case, there is no point in carrying out the control. From this, it can be said that quick response is required to maintain the maximum output point of the thermoelectric element.

  Further, from the viewpoint of ensuring quick response, it is extremely important how to set the initial state of the operation control of the thermoelectric element, that is, how to set the initial value. This is because, for example, at the start of operation of the thermoelectric generator, how fast the optimum state can be reached is affected by where the output current value is set. This point has been neglected in the past, and in practice, the initial value seems to be determined as if it were not. In each of Patent Documents 1 to 3, there is no description about this point.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermoelectric generator capable of almost always obtaining optimum output power through appropriate setting of initial values and the like.

[1]
In order to solve the above-described problem, the thermoelectric power generation device of the present invention is a thermoelectric power generation device that generates electric power using a high-temperature fluid discharged from a high-temperature fluid generation source, and converts the thermal energy of the high-temperature fluid into electrical energy. Thermoelectric elements to be converted, and control means for controlling the output of the thermoelectric elements with an initial current value determined according to the operating state of the high-temperature fluid generating source.

  According to the thermoelectric generator of the present invention, a part of the thermal energy of the high-temperature fluid (for example, exhaust gas) discharged from the high-temperature fluid generation source (for example, engine) can be extracted as electric energy. At this time, one side of the thermoelectric element is indirectly or directly in contact with the hot fluid, and the other side is indirectly or directly in contact with a cold fluid having a lower temperature (for example, water or air). Thus, a temperature difference is applied to the thermoelectric element, and it is possible to extract an electromotive force from the thermoelectric element due to this.

  In such a configuration and operation, for example, when a high-temperature fluid having a relatively high temperature is discharged from a high-temperature fluid generation source (hereinafter referred to as a “first case”), the thermoelectric element includes Since a relatively large temperature difference is applied, the output characteristics of the thermoelectric element are generally improved. Specifically, the maximum output power that can be extracted from the thermoelectric element becomes larger. On the other hand, when a high temperature fluid having a relatively low temperature is discharged from the high temperature fluid source (hereinafter referred to as “second case”), a relatively small temperature difference is applied to the thermoelectric element. As a result, the output characteristics of the thermoelectric element generally deteriorate. Specifically, the maximum output power that can be extracted from the thermoelectric element is smaller. In the first case, the output current value corresponding to the maximum output power is larger, and in the second case, the output current value is smaller. That is, the more preferable value of the operating current of the thermoelectric element varies depending on the operating state of the high-temperature fluid generating source.

  Here, in the present invention, the initial current value is determined according to such a change, that is, according to the operating state of the high-temperature fluid generating source. Therefore, for example, if the initial current value is set larger in the first case and smaller in the second case, the optimum value for obtaining the maximum output power in the initial state such as the start of operation of the thermoelectric element is obtained. It is possible to make the state appear more suitably. In addition, according to the present invention, such a preferable initial state is realized, and therefore, even when predetermined output control is performed on the thermoelectric element thereafter, the optimum operating state of the thermoelectric element can be quickly determined. Can be realized.

  The concept of “the operating state of the high-temperature fluid generation source” in the present invention specifically includes, for example, when the high-temperature fluid generation source is a so-called engine, the rotational speed of the engine or the exhaust from the engine. If the engine and the thermoelectric generator are mounted on a vehicle such as a four-wheeled vehicle, the speed of the vehicle is also included. According to the latter, the initial current value is determined by the vehicle speed of the vehicle.

  In addition, the “initial current value” of the present invention is determined as a current value at which the maximum output power based on the temperature difference in the operation state of the high-temperature fluid generating source is obtained or a current value close thereto. Is preferred. This is because the thermoelectric element can be operated in an optimal state or a state close to this from the initial state.

  In order to obtain the same effect, for example, when the “hot fluid generation source” referred to in the present invention is an engine, preferably, the “initial current value is determined according to the rotational speed of the engine”. More preferably, “the initial current value is determined to be larger when the engine speed is larger and smaller when the engine speed is smaller”. . Further, when the engine is mounted on the vehicle, the “engine speed” can be rephrased as “vehicle speed”.

[2]
In one aspect of the thermoelectric generator of the present invention, the control unit controls the output of the thermoelectric element based on at least one of the output current and the output voltage of the thermoelectric element.

  According to this aspect, since the output of the thermoelectric element is controlled based on the output current, the output voltage, or the output power obtained by multiplying these, the maximum output power can be extracted from the thermoelectric element. Such control can be suitably performed. In particular, in the present invention, the initial current value is determined according to the operating state of the high-temperature fluid generating source as described above. In other words, the thermoelectric element is operated near the output current value at which the maximum output power can be achieved from the beginning. Therefore, the time until the thermoelectric element can reach the maximum output power can be remarkably shortened by the control according to this aspect. Therefore, according to this aspect, it is possible to quickly cope with the case where the operating state of the high-temperature fluid generation source and the temperature of the high-temperature fluid change from moment to moment, or when these change transiently.

[3]
In another aspect of the thermoelectric generator of the present invention, the control means includes an output power corresponding to an output current of the thermoelectric element at a current time and an output power corresponding to an output current obtained by giving a predetermined deviation to the output current. Based on the comparison result, the output of the thermoelectric element is controlled.

  According to this aspect, control that can extract the maximum output power from the thermoelectric element is realized by a so-called “hill climbing method”. Therefore, the optimum state of the thermoelectric element can be realized relatively quickly. The “output current with deviation” can be expressed specifically as “I + ΔI” or “I−ΔI” if the output current of the thermoelectric element at the present time is expressed as “I”. Is possible. In this case, “ΔI” mentioned here corresponds to the “deviation” mentioned above.

[4]
In this aspect, the deviation may be configured to change according to time.

  According to such a configuration, the deviation changes according to time, more preferably according to the operating state of the high-temperature fluid generating source (the significance of which is as described above). In this way, for example, the hill-climbing method is further improved by changing or changing the deviation value between when the thermoelectric element is already operating near the maximum output point and when it is not. It can implement suitably.

  In order to realize this purpose better, for example, if the thermoelectric element is already operating at an operating point near the maximum output power, the deviation is smaller, otherwise the deviation is larger. Good. In this way, when the thermoelectric element is operating far from the maximum output point, convergence to the maximum output point can be realized more quickly, and once the maximum output point is reached, Divergence or oscillation at the maximum output point can be made difficult to occur.

  As described above, according to the present invention, it is possible to almost always obtain optimum output power from the thermoelectric element through appropriate setting of the initial value.

  Such operations, effects and other advantages of the present invention will become apparent from the embodiments described below.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a schematic diagram illustrating a configuration of the thermoelectric power generation system according to the present embodiment, and FIG. 2 is a schematic diagram illustrating a configuration example of a thermoelectric element. FIG. 3 is a diagram showing output characteristics of the thermoelectric element.

  In FIG. 1, the thermoelectric power generation system mainly includes a thermoelectric module 1, a power converter 2, and a battery 3. The thermoelectric module 1 includes a thermoelectric element, electrodes, wiring (all not shown in FIG. 1), and the like, and among these, the exhaust gas from the engine 150 shown in the figure is supplied to the thermoelectric element. The exhaust gas touches one side surface of the thermoelectric element indirectly or directly, thereby maintaining the one side surface at a relatively high temperature. On the other hand, the other side surface of the thermoelectric element is kept at a relatively low temperature by being indirectly or directly touched with water, air (not shown) or the like. Thereby, a temperature difference is applied to the thermoelectric element, and the thermal energy is converted into electric energy in the thermoelectric element (Seebeck effect).

  The thermoelectric element constituting the thermoelectric module 1 can be composed of, for example, a P-type semiconductor element and an N-type semiconductor element. In this case, more specifically, a Bi-Te system, a Pb-Te system, Appropriate ones can be selected from Si-Ge and the like. In the case of such a thermoelectric element, for example, as shown in FIG. 2, a P-type semiconductor element 11 and an N-type semiconductor layer element 12, a common electrode 13 disposed so as to be in contact with one side surface of both of these elements 11 and 12, and the like The individual electrodes 14a and 14b arranged so as to be in contact with the side surfaces of the electrodes, the wiring 15 connected to the individual electrodes 14a and 14b, and the like can be used. If the common electrode 13 side is the high temperature side (see reference numeral 16) and the individual electrodes 14a and 14b are the low temperature side (see reference numeral 17), the P-type semiconductor element 11 and the N-type semiconductor layer element 12 are used. An electromotive force V is generated therebetween, and a current I flows through the wiring 15.

  Such a thermoelectric element has output characteristics as shown in FIG. That is, FIG. 3 is a graph in which the horizontal axis represents the output current I of the thermoelectric element and the vertical axis represents the output power P. Each of the output powers P that change as the output current I from the thermoelectric element increases. Values are drawn along an upwardly convex curve. Therefore, there are maximum output points M1, M2 and M3 corresponding to the output current values I1, I2 and I3 on the curve. Further, ΔT1, ΔT2, and ΔT3 shown in FIG. 3 represent temperature differences applied to the thermoelectric elements, and a relationship of ΔT1 <ΔT2 <ΔT3 is established between them. That is, the output characteristic of the thermoelectric element changes due to the difference in temperature difference given to the thermoelectric element, and more specifically, the maximum output point also changes as the temperature difference increases. It is.

  In addition, although the thermoelectric element which consists of a semiconductor element was demonstrated above, this invention is not limited to this form, What kind of thing may be fundamentally employ | adopted about the structure of a thermoelectric element. For example, the thermoelectric element may be composed of different kinds of metal materials or ceramic materials, or may be composed of a semiconductor or an oxide thereof. When a thermoelectric element is constituted by these various materials, for example, the operating temperature range differs depending on the difference in the material. Therefore, when actually configuring the apparatus, a suitable material is appropriately selected in consideration of such circumstances. You may make it choose.

  Returning to FIG. 1, the power converter 2 includes a main circuit 21 and a controller 22. The main circuit 21 boosts and smoothes the voltage output from the thermoelectric module 1 until it reaches a predetermined value. Specifically, it consists of a known DC-DC converter. The controller 22 receives an output current I and an output voltage V from the thermoelectric module 1 and supplies an exhaust gas to the thermoelectric module 1 (more precisely, a rotation (not shown) attached to the engine 150). A rotation speed Ne of the engine 150 is received. The controller 22 determines a command value based on the output current I, the output voltage V, and the rotational speed Ne of the engine 150 and outputs the command value to the main circuit 21. In the main circuit 21, the output current or output voltage of the thermoelectric module 1 is changed according to this command value.

  The battery 3 is a known power storage device, and is charged by receiving output power generated from the thermoelectric module 1 and boosted by the main circuit 21. Although not shown in FIG. 1, in the present invention, instead of or in addition to the battery 3, an appropriate load that can be operated by the output power (for example, various motors, oil pumps, air conditioners). A compressor constituting the machine may be provided.

  The thermoelectric power generation system having such a configuration is operated as shown in FIGS. 4 to 6, for example, and as a result, the following effects can be obtained. FIG. 4 is a flowchart showing an operation example of the thermoelectric power generation system of the present embodiment, more specifically, a flow of processing for obtaining an optimum output from the thermoelectric module 1, and FIG. 5 is a step of FIG. FIG. 6 is an example of a map showing the relationship between the rotational speed and the initial current value used in obtaining the initial current value in S11, and FIG. 6 shows the operation mode of the thermoelectric element realized by the processing in step S13 and subsequent steps in FIG. It is explanatory drawing which shows this conceptually.

  First, the controller 22 reads the rotational speed Ne of the engine 150 (step S10 in FIG. 4). As described above, this can be obtained as a detection result of a rotation speed sensor (not shown) provided in the engine 150. Alternatively, other parameters such as the engine coolant temperature may be detected and estimated from the detection result to obtain the current rotational speed Ne.

  Next, an initial current value Iinit of the output current of the thermoelectric module 1 is obtained based on the read rotation speed Ne (step S11 in FIG. 4). The initial current value Iinit can be obtained based on, for example, a map as shown in FIG. 5 (see broken line arrow in the figure). In this figure, the initial current value IIinit is determined so as to increase monotonously as the rotational speed Ne increases. Therefore, the larger the rotation speed Ne, the larger the initial current value Iinit is selected. The power converter 2 is operated with the initial current value Iinit thus determined (step S12 in FIG. 4).

  As a result of such processing, the following effects are obtained. That is, the initial current value Iinit is obtained based on the rotational speed Ne. Specifically, the larger the latter, the larger the former (see FIG. 5). By the way, on the other hand, it can be said that the greater the rotational speed Ne, the greater the heat energy of the exhaust gas, and thus the higher the temperature of the exhaust gas. Then, since the temperature difference applied to the thermoelectric element becomes larger, it can be considered that the output power that can be taken out becomes larger (see FIG. 3). If so, it is desirable that the initial current value Iinit is set to increase as the rotational speed Ne increases. This is because, as shown in FIG. 3, the maximum output points M1, M2, and M3 corresponding to the temperature differences ΔT1, ΔT2, and ΔT3 (ΔT1 <ΔT2 <ΔT3) are I1, I2, and I3 that satisfy I1 <I2 <I3, respectively. It is because it is realized in. That is, if the current value is also increased as the temperature difference increases, the operating point of the thermoelectric element can be set closer to the maximum output point.

  For this reason, it is preferable that the initial current value Iinit is selected as I1, I2 or I3 shown in FIG. 3 or a value close thereto. That is, the map as shown in FIG. 5 is preferably determined in advance so that the initial current value Iinit is selected as such. By doing so, the operation in the optimum state (operation at the maximum output point) in the thermoelectric element or the operation at a point close to this is already realized from the initial state. .

  However, the heat energy of the exhaust gas also changes depending on the load applied to the engine 150. That is, even if the engine 150 is rotating at a certain number of revolutions, the heat energy of the exhaust gas is different if the load applied to the engine 150 is different, and thus the temperature difference applied to the thermoelectric element is also different. Accordingly, a map as shown in FIG. 5 in which the initial current value Iinit is selected as I1, I2 or I3 shown in FIG. 3, in other words, a map as shown in FIG. 5 in which the thermoelectric element operates at the maximum output point from the beginning (so to speak) It is generally difficult to have a “perfect” map. Therefore, since the initial current value Iinit is determined using the map shown in FIG. 5, it is generally expected that the thermoelectric element operates at a point having a certain degree of “deviation” from the maximum output point in the initial state. Become. However, such “displacement” is effectively eliminated by the processing in step S13 and subsequent steps described below.

  When the initial current value Iinit is determined as described above, the output power P1 (= I × V) is obtained from the values of the output current I and the output voltage V supplied from the thermoelectric module 1 supplied to the controller 22. (Step S13 in FIG. 4). The output current I obtained here may be referred to as “Iorigin” in the following for convenience of explanation.

Next, the operating current is changed (step S14 in FIG. 4). Specifically, ΔI taking a predetermined value is added to the current value Iorigin obtained in step S13. That is, the new current value I is
I = Iorigin + ΔI (1)
It becomes.

  Subsequently, the output power P2 (= I × V = (Iorigin + ΔI) × V) is obtained from the value of the output current I and the output voltage V obtained by adding ΔI (step S15 in FIG. 4).

Next, the operating current is changed again (step S16 in FIG. 4). Here, unlike the step S14, 2ΔI is subtracted from the current current value. That is, based on the above Iorigin, the new current value I is
I = Iorigin + ΔI−2ΔI = Iorigin−ΔI (2)
Therefore, when viewed from the original current value Iorigin, a value obtained by reducing ΔI from the Iorigin is taken as the operating current. Subsequently, the output power P3 (= I × V = (Iorigin−ΔI) × V) is obtained from the value of the output current I and the output voltage N obtained by subtracting 2ΔI (step S17 in FIG. 4).

When the output power P3 is obtained in this way, it is next determined whether or not P1 is larger than P2 obtained earlier and larger than P3 (step S19 in FIG. 4). . If it is determined that P1 is larger than both P2 and P3, the operating current is changed to I = I + ΔI (step S19 in FIG. 4; YES to step S21). According to this, since the current output current takes a value subtracted by ΔI from the original output current Iorigin by the processing of the previous step S16 (see equation (2)), in this step S21. The required new operating current is the same value as the original output current Iorigin as it is. That is,
I = (Iorigin−ΔI) + ΔI = Iorigin (3)
On the other hand, when it is determined that P1> P2 and P1> P3 are not satisfied, it is subsequently determined whether P3 is larger than P1 (step S19 in FIG. 4; NO to step S20). Here, when P3> P1 is not satisfied, that is, when P3 ≦ P1 is satisfied, the operating current is changed to I = I + 2ΔI (step S20 in FIG. 4; from NO to step S22). According to this, since the current output current takes a value subtracted by ΔI from the original output current Iorigin by the processing of the previous step S16 (see equation (2)), in this step S22. The required new output current I is a value obtained by adding ΔI to the original output current Iorigin. That is,
I = (Iorigin−ΔI) + 2ΔI = Iorigin + ΔI (4)
On the other hand, when P3> P1 is satisfied in step S20, the operating current is not particularly changed unlike the above-described cases. That is, in this case, the value subtracted by ΔI from the original output current Iorigin is maintained as it is by the process of step S16. That is,
I = Iorigin−ΔI (5)
When the above processes are completed, the process returns to step S13, and processes after the calculation of the value of the output power P1 are started again. Thereafter, these processes are repeatedly executed.

  Through the processing as described above, the thermoelectric element can be operated at the maximum output point. This will be described below with reference to FIG. FIG. 6 is a graph showing the output characteristics of the thermoelectric element with the output current on the horizontal axis and the output power on the vertical axis, the meaning of which is exactly the same as FIG. 3 (FIG. 6 is similar to FIG. Only the effect of the difference in temperature differences ΔT1, ΔT2 and ΔT3 is not shown).

  In FIG. 6, first, when the current value Iorigin obtained in step S <b> 13 matches the current value corresponding to the point P <b> 1 included in the ellipse indicated by the symbol B <b> 1 in the drawing (hereinafter referred to as “case I”) ), The operating current Iorigin + ΔI (equation (1)) realized in step S14 coincides with the current value corresponding to the point P2 located to the right of the point P1, and in step S16. The realized operating current Iorigin−ΔI (equation (2)) matches the current value corresponding to the point P3 located on the left side of the point P1. In this case, P1 is determined to be larger from both P2 and P3. Therefore, in FIG. 4, the process proceeds from step S19; YES to step 21, and as a result, the operating current is Iorigin. (Equation (3)). Therefore, the maximum output point is taken in the thermoelectric element.

  If the current value Iorigin matches the current value corresponding to the point P1 included in the ellipse indicated by the symbol B2 in the figure (hereinafter, sometimes referred to as “case II”), the point P1, Although the arrangement relationship between the points P2 and P3 (the points P3, P1, and P2 are arranged in order from the left in the figure) is the same as described above, P1 is larger than P3 (P1> P3) but smaller than P2 ( P1 <P2) is different from the above. Accordingly, in FIG. 4, the process proceeds from step S19; NO to step S20, and further from step S20; NO to step S22. As a result, the operating current is Iorigin + ΔI ((4) formula). Therefore, in the thermoelectric element, the highest output power value (point P2) among these three points is taken. On the other hand, when the current value Iorigin matches the current value corresponding to the point P1 included in the ellipse indicated by the symbol B3 in the drawing (hereinafter sometimes referred to as “case III”), P1 is obtained from P3. It is smaller (P1 <P3) and larger than P2 (P1> P2). In FIG. 4, the process proceeds from step S19; NO to step S20, and further proceeds to step S20; YES. As a result, The operating current is Iorigin−ΔI (Equation (5)). Therefore, also in this case, the thermoelectric element has the highest output power value (point P3) among these three points.

  And in these cases II and III, when the process after step S13 is repeatedly performed, the output power of the thermoelectric element approaches the maximum output point. For example, in the case II, when the process after step S13 is performed again following the process described above, the point P2 is regarded as a new point P1, and in this process, the new point P1 is determined. As shown in the ellipse B2 in FIG. 6, P3, P1, and P2 are arranged in order from the bottom in the figure. Therefore, since P1> P3 and P1 <P2 are also established at this time, the highest output power value (new point P2) is taken. Hereinafter, it is clear that the same output is repeated until the maximum output point is reached (the operating point gradually rises along the slope of the graph in this way, and this method is called the “hill climbing method”. be able to.).

  This is basically the same as in case III, but the direction of the three points is reversed (that is, the three points are advanced toward the upper left in the figure). To occur.

  As described above, in cases II and III, the maximum output point that can be achieved in the thermoelectric element can be achieved in the near future. In case I, since the maximum output point is achieved if the current output current is maintained at the beginning, the point P1 is selected.

  By performing the processing as described above, according to the thermoelectric power generation system of the present embodiment, the following effects can be obtained. That is, first, by performing the processing from step S13 in FIG. 4, the thermoelectric module 1 constituting the thermoelectric power generation system of the present embodiment is almost always operated at an optimum efficiency, and as a result, Optimal output power can be obtained. Therefore, the battery 3 is efficiently charged. Such an effect is particularly effectively enjoyed when the temperature of the exhaust gas supplied to the thermoelectric power generation module 1 changes from moment to moment or when it changes transiently.

  In the present embodiment, in particular, since the initial current value Iinit is determined based on the engine speed Ne (see step S11 and step S12 in FIG. 4), the above effect is further promoted. . This is because, as already described, the initial current value Iinit is set to be larger as the rotational speed Ne increases, in other words, as the temperature difference applied to the thermoelectric element increases. The operating point in the initial state of the thermoelectric element can be set to the maximum output point or a point close thereto. Then, after such a favorable initial state is realized, the processing after step S13 in FIG. 4 is performed. Therefore, in this embodiment, the time until the thermoelectric element reaches the optimum operating point. Can be greatly shortened.

  In the above embodiment, only the rotational speed Ne is referred to when the initial current value Iinit is determined, but the present invention is not limited to such a form. For example, when the engine 150 shown in FIG. 1 is mounted on a vehicle such as a four-wheeled vehicle, the operation speed of the vehicle, that is, the vehicle speed can be used in addition to or instead of the rotation speed Ne. This vehicle speed, like the rotation speed Ne, also implies an increase in exhaust energy, which also implies a higher temperature of the exhaust gas, which further increases the temperature difference ΔT applied to the thermoelectric element. Since it can be implied, the same effect as described above can be obtained. Further, the temperature of exhaust gas discharged from the engine 150 may be used in addition to or instead of the rotational speed Ne or the vehicle speed.

  Further, in the above embodiment, the thermoelectric element can be operated efficiently only by performing the processing shown in FIG. 4, so what is the actual temperature difference ΔT applied to the thermoelectric element? It is not always necessary to know in advance. That is, since the process itself of FIG. 4 does not change the property depending on the temperature, it is not particularly necessary to know the temperature difference ΔT. Therefore, it is not necessary to provide a special device (for example, a temperature sensor) for knowing the temperature difference ΔT. However, if the actual temperature difference ΔT applied to the thermoelectric element is known, there is a possibility that the processing shown in the present embodiment can be performed more beneficially. Therefore, the present invention does not intend to positively exclude the form in which the temperature difference ΔT is known or a device for that purpose is provided.

  Furthermore, in the above-described embodiment, an implicit premise that ΔI used in the processing in step S13 and the subsequent steps is constant is set (see FIG. 6), but the present invention is not limited to such a form. For example, with respect to ΔI used in the processing in step S13 and subsequent steps, a configuration or processing that changes this according to time can be adopted. More specifically, for example, ΔI can be changed using FIGS. 7 and 8 as follows. FIG. 7 is a map showing the relationship between the speed (vehicle speed) of the vehicle and the maximum output power corresponding to the vehicle speed when the engine 150 shown in FIG. 1 is mounted on a vehicle such as a four-wheeled vehicle. is there. FIG. 8 is a map showing the relationship between ΔI and the difference between the current output power and the maximum output point.

  First, in step S10 of FIG. 4, after the engine 150 shown in FIG. 1 knows the vehicle speed V of a vehicle such as a four-wheeled vehicle (or, as shown in FIG. 4, it is of course possible to know the rotational speed Ne). The maximum output power Pmax corresponding to the vehicle speed V is obtained using the map of FIG. 7 (see the broken line in the figure). In FIG. 7, the vehicle speed V is taken on the horizontal axis, and the maximum output power Pmax is taken on the vertical axis, and the latter increases proportionally as the former increases. In addition, instead of the map of FIG. 7, the maximum output power Pmax is derived from a drawing similar to FIG. 5 (the horizontal axis is the vehicle speed, the vertical axis is the current value at which the maximum output power and power close thereto are obtained) and FIG. 3. Can also be requested. Further, when using the rotation speed Ne instead of the vehicle speed V, for example, a map between the rotation speed and the maximum output power may be prepared instead of FIG.

  Next, using the maximum output power Pmax thus obtained and the current output power P1 obtained in step S13 of FIG. 4, a difference ΔP between them is obtained (ΔP = Pmax−P1). Note that since the current output power P1 is generally considered not to reach the maximum output power Pmax, ΔP is normally a positive number (in case of reaching, it is naturally “0”).

  Then, using this ΔP and the map of FIG. 8, ΔI to be used at that time is obtained (see the broken line in the figure). In FIG. 8, ΔP is taken on the horizontal axis and ΔI is taken on the vertical axis, and the latter increases monotonously as the former increases. ΔI obtained in this way is larger when ΔP is large and smaller when ΔP is small. In other words, ΔI is larger when the current output power P1 is further away from the preferred maximum output power Pmax, and ΔI is smaller when closer. Therefore, when the current output power P1 is within the ellipse B1 shown in FIG. 6, that is, when ΔP is small, ΔI is taken small, so that the oscillation around the point P1 (from P1) The movement from P2 to P3 (see arrow in the figure) becomes smaller. On the other hand, when the current output power P1 is within the ellipses B2 and B3 shown in the figure, that is, when ΔP is large, ΔI is taken large, so the movement of the point P1 becomes larger and maximum. Reaching the output point will be achieved more quickly.

  As described above, if ΔI is changed according to time (more specifically, “ΔI is changed according to the operating state of the high-temperature fluid generating source”), convergence to the maximum output point is achieved. It can be realized more quickly, and once the maximum output point is reached, divergence or oscillation at that point can be made difficult to occur. Note that such processing may be performed by inserting it between step S13 and step S14 in FIG. 4, for example.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification, and a thermoelectric power generator with such a change Is also included in the technical scope of the present invention.

It is a schematic diagram showing the composition of the thermoelectric power generation system concerning this embodiment. It is a schematic diagram which shows one structural example of a thermoelectric element. It is a figure which shows the output characteristic of the said thermoelectric element. It is a flowchart which shows the operation example of the thermoelectric power generation system of this embodiment, and the flow of the process for obtaining the optimal output from a thermoelectric module more specifically. It is an example of the map which shows the relationship between the rotation speed utilized when calculating | requiring an initial stage current value in step S12 of FIG. 4, and an initial stage current value. It is explanatory drawing which shows notionally the operation | movement aspect of the thermoelectric element implement | achieved by the process after step S13 of FIG. 2 is a map showing the relationship between the speed (vehicle speed) of the vehicle and the maximum output power corresponding to the vehicle speed when the engine 150 shown in FIG. 1 is mounted on a vehicle such as a four-wheeled vehicle. It is a map showing the relationship between the present output power and the difference between the maximum output points and ΔI.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Thermoelectric power generation module 11 ... P-type semiconductor element 12 ... N-type semiconductor element 13 ... Common electrode 14a, 14b ... Individual electrode 15 ... Wiring 2 ... Power converter 21 ... Main circuit 22 ... Controller 3 ... Battery 150 ... Engine M1, M2, M3 ... Maximum output point Iinit ... Initial current value

Claims (4)

A thermoelectric generator that generates electric power using a high-temperature fluid discharged from a high-temperature fluid source,
A thermoelectric element that converts thermal energy of the high-temperature fluid into electrical energy;
And a control means for controlling the output of the thermoelectric element with an initial current value determined according to the operating state of the high-temperature fluid generating source. The control means includes
The thermoelectric generator according to claim 1, wherein an output of the thermoelectric element is controlled based on at least one of an output current and an output voltage of the thermoelectric element. The control means includes
Controlling the output of the thermoelectric element based on the comparison result between the output power corresponding to the output current of the thermoelectric element at the current time and the output power corresponding to the output current obtained by giving a predetermined deviation to the output current. The thermoelectric power generator according to claim 1 or 2. The thermoelectric generator according to claim 3, wherein the deviation changes according to time.

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